T.SHIVAKUMARKottam institute of pharmacyJNTU, A.P

INTRODUCTIONCoated tablets are defined as tablets covered with one or more layers of mixture of various substances such asNatural Or Synthetic Resins Gums Inactive And Insoluble Filler, Sugar Plasticizer Polyhydric Alcohol Waxes Authorized Colouring Material And Some Times Flavoring Material.

Therapy

Avoid irritation of oesophagus and stomach Avoid bad taste Avoid inactivation of drug in the stomach Improve drug effectiveness Prolong dosing interval Improve dosing interval Improve patient compliance

II. Technology

Reduce influence of moisture Avoid dust formation Reduce influence of atmosphere Improve drug stability Prolong shelve life

III. Marketing

Avoid bad taste Improve product identity Improve appearance and acceptability

Tablet coating is the application of coating composition to moving bed of tablets with concurrent use of heated air to facilitate evaporation of solvent.Basic principle of tablet coating

Sugar coatingFilm coatingEnteric coatingControlled release coatingSpecialized coating Compressed coating Electrostatic coating Dip coating Vacuum film coating

EQUIPMENTS FOR TABLET COATINGThree general types of equipments are available

1.Standard coating pan

e.g., Pellegrino pan systemImmersion sword systemImmersion tube system

2.Perforated pan system

e.g.,Accela cota systemHicoater systemGlattcoater systemDriacoated system

3.Fluidized bed coater

POLISHING

Standard Coating PanImmersion-tube system Glatt Immersion sword system Pellegrini pan system STANDARD COATING PAN

PERFORATED PANSAccela cota systemHi-coater system

PERFORATED PANS (continue)Dria coater panGlatt coater

FLUID BED COATING SYSTEMS

1. Film coating

2. Sugar coating

3. Press coating

Main coating processes

Traditionally sugar coatings formed the bulk of coated tablets but today film coatings are the more modern technology in tablet coating.Description of tablets: Smooth, rounded and polished to a high gloss.Process: Multistage Process involving 6 separate operations.

Example of sugar coated tablets Sugar coating

MULTISTAGE PROCESSSealing tablet core- application of a water impermeable polymer such as Shellac, cellulose acetate phthalate and polyvinyl acetate phthalate, which protects the core from moisture, increasing its shelf life.

Sub coating -by adding bulking agents such as calcium carbonate or talc in combination with sucrose solution.

Smoothing process -remove rough layers formed in step 2 with the application of sucrose syrup.

Colouring - for aesthetic purposes often titanium based pigments are included.

Polishing - effectively polished to give characteristic shine, commonly using beeswax, carnauba wax.

Printing -indelible ink for characterisation.

1- Sealing (Waterproofing)This involved the application of one or more coats of awaterproofing substance in the form of alcoholic spray, such as pharmaceutical Shellac (traditionally) or syntheticpolymers, such as CAP.( Unless a modified-release feature needs to be introduced, the amount of the sealing coat applied should be carefully calculated so that there is no negative effect on the drug release characteristics in case of immediate release product.)

(WHY Sealing?)a- Sugar-coatings are aqueous formulations which allowwater to penetrate directly into the tablet core and thuspotentially affecting product stability and possibly causingpremature tablet disintegration.b- Application of many coats of partially or completelywater-insoluble polymers in this step, enables sugar-coatedproduct to exhibit modified-release pattern (extendedreleaseor delayed "enteric"- release characteristics).

2. Subcoating- Large quantities of sugar-coatings are usually applied to the tablet core (typically increasing the tablet weight by ( 50- 100%) WHY? In order to round off the tablet edge. Much of this material build-up occurs during this stage and is achieved by adding a bulking agent such as Calcium carbonate, to the sucrose solution.

- Antiadherents e.g. Talc may be added after partial drying to prevent sticking of the tablets together.

3- SmoothingThe subcoating stage results in tablets with rough surfaces. To facilitate the color application (which requires smooth surface), subcoated tablets are smoothed out by a thick sucrose syrup coating.

4- ColoringColor coatings usually consist of thin sucrose syrup containing the requisite coloring materials. (water-soluble dyes or water-insoluble pigments may be used) This step must be done into a clean pan deprived of any residues from the previous operations.

5- PolishingAfter the coloring step, the tablet surfaces tend to be smooth but somewhat dull in appearance. To achieve glossy finish, final stage involving application of waxes (beeswax carnuba wax) is employed.

6- PrintingDifferent tablets could be identified by manufacturer' logo, product name, dosage strength or other appropriate code. For sugar-coated tablets, such identification could be only achieved by printing process using special edible inks.

Brufen POMAvailable in 200mg and 400mg strength

Premarin POMConjugated oestrogens 625mcg (maroon) and 1.25mcg (yellow)

Colofac PMebeverine hydrochloride 100mg Round, white, sugar coated

Kalms GSL45mg Hops powder,90mg Gentian powdered extract, and 135mg Valerian powdered extract

EXAMPLE OF SUGAR COATED TABLETS

SUGAR COATED PROCESS

Modern approach to coating tablets, capsules, or pellets by surrounding them with a thin layer of polymeric material. Description of tablets: Shape dictated by contour of original core. Process: Single stage process, which involves spraying a coating solution containing the following;PolymerSolventPlasticizerColourantThe solution is sprayed onto a rotating tablet bed followed by drying, which facilitates the removal of the solvent leaving behind the deposition of thin film of coating materials around each tablet.

FILM COATING

Advantages Produce tablets in a single step process in relatively short period of time. Process enables functional coatings to be incorporated into the dosage form.

Disadvantages There are environmental and safety implications of using organic solvent as well as their financial expense.Types of film coatingImmediate release

Modified release

Polymer

* 2.Plasticizers Plasticizers are generally added to film coating formulations to modify the physical properties of the polymer to make it more usable. One important property is their ability to decrease film brittleness. Examples of plasticizers are:polyols, such as polyethylene glycol 400organic esters, such as diethyl phthalateoils/glycerides, such as fractionated coconut oil.In general, only water-miscible plasticizers can be used for aqueous-based spray systems.

*3.Colourants Any permitted colourants in a film coat formula are invariably water-insoluble colours (pigments). Pigments have certain advantages over water-soluble colours: they tend to be more chemically stable towards light, provide better opacity and covering power, and optimize the impermeability of a given film to water vapour.

Examples of colourants are: iron oxide pigments titanium dioxide aluminum Lakes.

*4.SolventsModern techniques now rely on water as a polymer solvent because of the significant drawbacks that readily became apparent with the use of organic solvents.

MATERIAL USED FOR FILM COATING

Nonenteric materials : e.g.Hydroxypropyl methylcellulose (HPMC)Methylhydroxy ethyl cellulose (MHEC)Ethylcellulose (EC)Hydroxypropyl cellulose (HPC)Polyvinyl pyrrolidone (PVP)Sodium carboxymethyl cellulose (Sod. CMC)Polyethylene glycols (PEG)Acrylate polymers e.g. Eudragit EEnteric materials: e.g.Cellulose acetate phthalate (CAP)Acrylate polymers (Eudragit L, S)Hydroxypropyl methylcellulose phthalate (HPMCP)Polyvinyl acetate phthalate (PVAP)

The vast majority of film coated tablets are produced by a process which involves spraying of the coating material on to a bed of tablets. Accela Cota is one example of equipment used for film coating.Accela Cota

Accela Cota

Film coating Tablet appearanceRetains shape of original core Small weight increase of 2-3% due to coating material logo or break lines possible Process Can be automated e.g. Accela CotaEasy training operation Single stage processEasily adaptable for controlled release allows for functional coatings.

Sugar coating Tablet appearanceRounded with high degree of polishLarger weight increase 30-50% due to coating materialLogo or break lines are possible Process Difficult to automated e.g. traditional coating pan Considerable training operation required Multistage process Not able to be used for controlled release apart from enteric coating.

DIFFERENCE BETWEEN FILM COATNIG & SUGAR COATING

use of compression to form coat around a pre-formed core

used mainly to separate chemically incompatible materials also dual release patterns possible

PRESS COATING

*To separate chemically incompatible materials, one or more being placed in the core and the other(s) in the coating layer. However, there is still an interface contact left between the two layers. In cases where even this is important then the process of pre coating can be taken one stage further. It is possible to apply two press coatings to a tablet core using suitable equipment. This equipment produces press-coated tablets with perfect separation between active core and coating, as the two can be separated by an inert middle layer.press coating is used

**

Advantages Produce tablets with characteristically smooth rounded contour with even colour coverageDisadvantages Time consuming process Functional coatings are usually possible other than enteric coatings 30-50% weight increase due to coating material logo or break lines not possible .

*LINKS OR DIAGRAMS OF TRADITIONAL COATING PAN AND ACCELA COTA

2) Reasons for film coating include:AppearanceTo change the color, for branding purposes or other aesthetic reasonsStabilityTo protect the active ingredient from moisture, light, and/or the acidic environment of the stomachTaste/odor MaskingTo provide an easy to swallow tablet without the bitter taste of many activesRelease characteristicsMany film coating materials have functional properties which enable the creation of sustained or delayed (enteric) release dosage forms**http://www.glatt.com/e/01_technolo http://www.glatt.com/e/01_technologien/01_04_08.htm (picture from - obtained from google search image accela cota